Much attention has been applied in the recent past to improving the appearance of tooth coloured filling materials, with a wide range of composite resin and porcelain filling materials now available. The aim has been to make these restorative dental filling materials as similar in appearance to tooth structure as possible. The intention is that when a tooth is fractured (traumatically), decayed, severely worn or otherwise damaged, then composite resin and porcelain filling materials with their corresponding adhesives, may be used to restore the tooth to its pre-damaged state. A primary goal has thus been to make the filling “invisible” so that once restored, the tooth appears to be intact, as the restoration is difficult to see visually.
As a result, filling materials have evolved to the point whereby they mimic tooth structure in terms of opacity, hue and chromaticity. In the case of some of the higher end composite and porcelain materials available, these restoratives will also provide some fluorescence and opalescence properties as well. At the present time, it is possible to restore a badly broken down tooth with multiple layers of varying coloured composite filling materials, such that it is very difficult to distinguish between natural tooth structure and the prosthetic material. Porcelain restorations manufactured by a skilled dental ceramist can also be very difficult to distinguish from natural tooth structure.
However, dental restorations do not last indefinitely, and eventually all composite and porcelain materials begin to wear, break down, leak at their margins or lose their shine and become discoloured. Accordingly, there is a need to remove and/or replace composite and porcelain fillings from teeth. A major concern for the clinician is that the process of removing a filling will result in more tooth structure being ground away and hence more damage occurring to the tooth. With the increasing use of tooth-coloured fillings, which can replicate the optical properties of natural tooth structure, it can be extremely difficult to be certain that no such fillings have escaped recognition or have been misidentified during a clinical examination or when removing an existing filling to access underlying decay. Such fillings are not unambiguously visible. Differences in fluorescence provide such a method for identifying tooth coloured fillings. Tooth-coloured restorative materials, dental caries and calculus have a different fluorescence signature from healthy tooth structure.
In the case of modern composite and porcelain filling materials, the overall match in shade between the remaining natural tooth structure and the filling material may be very good, making it difficult to distinguish between restorative material and remaining enamel and dentine. There is the very real risk that excessive tooth structure will be cut or ground away from the natural tooth during removal of an existing filling. The consequence is that the residual tooth will become weaker and may even suffer damage to its pulp (nerve). Additionally, the time it takes a clinician to continuously stop, dry and visualise the remaining tooth-filling interface, increases the length of time needed to perform the procedure and hence the appointments become longer or greatly rushed. There is also the potential problem of not visualising all of the remaining old filling material in the tooth, and hence leaving some behind. This in turn may result in bacteria remaining in the tooth after the new restoration is placed or may compromise bond strengths of the new filling that is subsequently placed, and both of these events may cause further problems post-operatively.
Fluorescence can be used in the detection of fillings because the light-induced fluorescence signals from tooth coloured fillings differ from those for normal dental enamel. The fluorescence emission properties of healthy dental enamel were characterized by Angmar-Mansson and others at the Karolinska Institute in the late 1980's and early 1990s. Visible blue light (470 nm) was shown to elicit yellow fluorescence from the calcium-phosphate bonds in hydroxyapatite. (Sundstrom et al., 1985, Swed Dent J. 9:71-80; Angmar-Mansson et al., 1996, Eur J Oral Sci. 104: 480-485) Previous work on fluorescence identification of tooth coloured fillings has used separate external light sources (Stimpson 1985, Acta Med Leg Soc (Liege) 35:278-284. Pretty et al., 2002, J Forensic Sci. 47:831-6) rather than a diagnostic light which is incorporated into a device for cutting or cleaning, as in the current invention.
Another major problem facing the dental clinician relates to caries (decay) in a tooth, either in the form of a new lesion, or recurrent caries beneath a previously placed composite, porcelain or other restoration. Recurrent decay beneath existing fillings poses a particular problem in that any excessive removal of tooth tissue weakens the remaining tooth structure and makes injury to the dental pulp more likely. In order to treat the tooth, the dentist must visualise all of the decay to facilitate its mechanical debridement with a dental handpiece and bur, or with another type of cutting technology, such as a diamond coated tip in an ultrasonic handpiece. The technique that is employed under local anaesthetic is to visualise the discoloured tooth structure, assume it is decay (either by its visualised colour or by tactile feel), and then the tooth is ground with the bur to remove this infected dentine. However, under normal lighting conditions, decayed dentine does not always appear significantly different to the surrounding sound tooth structure, and tactile probing to determine the extent of decay can be very subjective. A very real risk exists that an overly zealous technique may be applied by the dental clinician and that too much tooth structure will be removed in the operative process. This will weaken the tooth and may lead to pulp complications as previously described. Alternatively, and perhaps worse, it is also possible that not all of the decayed tooth structure will be identified by the dentist, and that some decay may be left behind by not removing enough tooth structure before the new filling is placed. A method which can assist the dental clinician in determining that infected dentine still remains will result in more conservative tooth cavity preparations.
Tooth decay can proceed at varying rates in different individuals and decay that is deep and rapidly advancing may be difficult to fully detect by normal visual and tactile methods alone. Using dental X-rays can assist in detecting the presence of decay beneath fillings, but this method cannot assist the dental clinician during the procedure, once the filling has been removed and they are then faced with the decision regarding how much natural tooth tissue to remove in the various areas of the cavity. Accordingly, other aides have been used by the clinician to determine the boundary between sound tooth structure and infected diseased structure, so that only the latter is removed. Colour, disclosing dyes, tactile feel, laser light and short wavelength light fluorescence, and resistance to the drill are all techniques that are used.
One example, “Carisolv”, is a chemical solution based on sodium hypochlorite with amino acids which attacks that part of the tooth which is decayed. The net result is that demineralised parts of the tooth are softened and a dedicated bur is then used to selectively remove the decayed tooth structure, hopefully without damage to the deeper, sound parts of the tooth.
Another approach has been to use a caries (decay) detection dye based on basic fuchsin or acid red dyes. This material is applied to the tooth and will stain caries tissue red and make its appearance distinct from the surrounding tooth. This technique is not particularly specific and may lead to more tooth structure being removed than is necessary. In some instances, red dye will remain in the tooth after the procedure, which may in turn leave a pink hue to the finished filling.
The process of fluorescence occurs when incident light applied to a structure is emitted at a longer wavelength, with some conversion of the incident energy into heat. The process of fluorescence has been exploited for a range of diagnostic methods, for example the detection of hidden fissure caries by the DiagnoDENT device, in which visible red laser light (655 nm wavelength) elicits fluorescence in the near infrared region (700-900 nm). Because bacterial products such as porphyrins evoke the fluorescence, the intensity of the emitted light is related to the volume of the carious lesion. Similar fluorescence processes occur with porphyrins in dental calculus, where ultraviolet light elicits red fluorescence, and visible red light elicits near infrared emissions. This process is best termed POSITIVE fluorescence, in that the desired target (in this case the caries or dental calculus) elicits the fluorescence signal.
Laser-light based technologies such as the “Diagno-Dent” have been used to measure the near infrared fluorescence signal of bacteria present in the tooth, identifying regions that do not fluoresce strongly in a manner consistent with sound dentine. This device can be used as a diagnostic tool to identify subsurface areas of a tooth where decay is occurring, but cannot be seen from the surface. Following on from this concept, the application of short wavelength light via a dedicated, stand-alone instrument such as the “Sopro Aceon” have also been proposed as a means of illuminating a decayed tooth and stimulating fluorescence of the decayed region. The differential fluorescence between diseased and healthy tooth structure then assists the clinician to distinguish between boundaries in the tooth, allowing more careful removal of only the decayed tooth structure, leaving the sound part of the tooth alone. For light wavelengths from 400 to 420 nm, carious lesions with cavitations in dentine containing bacteria show emissions at 600-700 nm typical for porphyrin compounds (Buchalla, 2005, Caries Res. 39:150-6). The bacteria and their metabolic products induces an increase in the absorption in the UVA and visible blue spectral region from 350-420 nm, which results in the appearance of a fluorescence signal in the visible red spectral region at 590-650 nm (Borisiva et al., 2006, Lasers Med Sci. 21:34-41).
Yet another problem that exists pertains to the thorough and complete removal of dental plaque and calculus (tartar) from teeth during a scale and cleaning hygiene appointment. Whilst older, mature calculus that has been on the teeth for a long time may begin to become dark in colour and is readily visible, newer plaque and calculus deposits, as well as the remnants of large deposits that may have been incompletely scaled off the teeth, are often light in colour, frequently matching the shade of the teeth themselves. This can make it very difficult to adequately visualise the bacterial deposits that need to be removed from the teeth. As ultrasonic scaling techniques are performed with a copious water spray, visualisation of the field of cleaning can be compromised, leading to insufficient removal of the plaque and calculus.
This problem can be overcome in part by frequently stopping the ultrasonic scaling procedure and thoroughly drying the teeth, in an attempt to observe the remaining plaque and calculus, as this will dry to a “frosty” or “sandy” appearance relative to the shiny natural tooth structure. However, it is often difficult to completely dry the teeth in all parts of the mouth, and this also takes time and draws out the appointment duration. A more ready means of identifying the plaque and calculus on the teeth at the time of debridement would be preferred.
As mentioned previously, a disclosing dye may be applied to the teeth prior to scaling and cleaning. The plaque and calculus will then stain pink or red.
However, this can lead to excessive staining of the mouth and lips as a whole and is not a technique that is preferred by patients. An alternative approach is to use the concept of fluorescence of bacterial plaque and calculus and hence shining a light of specific wavelength directly onto the teeth to be cleaned. This causes red fluorescence of the bacterial deposits, helping the clinician to identify their location, prior to cleaning. However, this technique requires the frequent and repeated stopping of the scaling process and shining of the light on the teeth in order to have some efficacy. This is an inconvenient process and also contributes to considerable time delays in the scaling and cleaning appointment.
The ultraviolet and visible blue wavelengths are desirable for fluorescence diagnosis. Under UVA excitation (363.8 nm), enamel has a fluorescence spectrum which has the shape of a wide band, with a maximum of 450 nm (characteristic of a blue-green shade) and a slow decrease up to 680 nm. The enamel fluorescence does not depend on the colour of the tooth. Dentine has a distribution spectrum which is similar to that of enamel but is three times fuller. The spectra of dental porcelains comprises a wide band due to transition metals, and fine lines due to rare earth elements (terbium and europium). When the saturation degree of the ceramic increases, its fluorescence colour varies due to the relative increase in the amplitude of the lines in relation to the bands. Thus, when the porcelain colour is more saturated, its fluorescence colour becomes greener (Stimpson et al., 1985, supra).
With regard to identifying deposits of dental plaque or dental calculus, under UVA and visible blue light, positive red fluorescence from deposits of mature dental plaque on the surface of teeth, restorations, or dental appliances can be identified. This can be done to assist in their controlled removal by a powered scaler, as well as being used as an aid in oral hygiene education. Following tooth cleaning, residual deposits of plaque and calculus appear as red fluorescing areas (Kühnisch et al., 2003, Int Poster J Dent Oral Med 5: 177). Red fluorescence is associated with mature dental plaque on dentures. The maturity of dental plaque, rather than the presence of cariogenic streptococci, is the basis for the red fluorescence (Coulthwaite et al., 2006, Caries Res. 40:112-6).
Many of the aforementioned analytical and examination techniques available to dentists, and other techniques, are reviewed in Walsh, 2008, Australasian Dental Practice 19 47.